1. Field of the Invention
The present invention relates to a method for producing an iridium complex by the use of a novel intermediate. The iridium complex obtained by the producing method of the present invention can be utilized in an organic electroluminescence device and a display apparatus. More specifically, the method for producing an iridium complex of the present invention uses an auxiliary ligand having an unstable 4-membered ring structure as an intermediate, thereby enabling reaction to proceed at a low temperature to produce an iridium complex with a high yield.
2. Description of the Related Art
With organic light emission devices, an example in an early reference is known in which a voltage is applied to an evaporated anthracene film to cause a light emission (Thin Solid Films, 94 (1982) 171: non-patent reference 1). In recent years, the organic light emission devices have been found to have advantages such as the easiness of larger area formation in comparison with inorganic light emission devices, a possibility of obtaining desired light emission color due to the development of various new materials and a drivability at a low voltage, and is now actively developed for realizing light emission devices fast in response and high in efficiency, including the development of materials.
The organic electroluminescence (EL) device generally has a structure in which a pair of upper and lower electrode layers and an organic material layer interposed therebetween including a light emission layer are formed on a transparent substrate, as described in Macromol. Symp. 125, 1-48 (1997) (non-patent reference 2).
In addition to the conventional light emission utilizing fluorescence ascribable to a transition from a singlet exciton to a ground state, devices are recently investigated utilizing phosphorescent light emission through a triplet exciton, as typified by D. F. O'Brien et al., Improved energy transfer in electrophosphorescent device, Applied Physics Letters, Vol. 74, No. 3, p 422 (1999) (non-patent reference 3) and by M. A. Baldo et al., Very high-efficiency green organic light-emitting devices based on electrophosphorescence, Applied Physics Letters, Vol. 75, No. 1, p 4 (1999) (non-patent reference 4). These references principally utilize an organic layer of a 4-layered structure which is composed of, from the anode side, a hole transport layer, a light emission layer, an exciton diffusion preventing layer and an electron transport layer. The materials being used include a carrier transport material and a phosphorescent material Ir(ppy)3 shown below.

Light emission from an ultraviolet region to an infrared region is possible by changing the types of fluorescent organic compounds, and various compounds are recently being actively investigated.
In addition to the organic light emission devices utilizing low-molecular materials as described above, an organic light emission device utilizing a conjugated polymer is reported by a group at Cambridge Univ. (Nature 347,539 (1990), non-patent reference 5). This report confirmed light emission from a single layer by forming a film of polyphenylenevinylene (PPV) by means of a coating system.
In this manner, the organic light emission devices are recently showing remarkable progress to make it possible to achieve a thin light-weight light emission device with features of a low applied voltage, a high luminance, a wide variety of light emission wavelengths, and a high-speed response, thus suggesting possibilities of wide applications.
However, under the present conditions, a light output higher in luminance and higher conversion efficiency are being sought. In addition, various problems remain unsolved concerning durability, such as changes over time during long-term service, and concerning deterioration due to oxygen-containing atmospheric gases or moisture. Also, at present, due to the fact that a temperature of about 200° C. is required at the time of production, productivity is not very high.